Azure Migrated Server - SMTP Traffic Bypassing NAT Gateway

abeer hayat khan 0

I have migrated an on-prem server to the Azure cloud.

Machine Details: Name: Horizon Private IP: 192.168.1.10 Subnet: Development NAT Gateway: azure-nat Public IP on NAT: 104.233.121.78

When surfing the web, the public IP check returns source IP as 104.233.121.78. When sending SMTP traffic to EOL Relay the Source address in the local SMTP logs is 513.95.218.52. It seems that the SMTP (or custom TCP/UDP Port 25) traffic is not adhering to the Nat Gateway when it should.

Can you advise why the SMTP traffic is originating from the Random MS Cloud address and not the NAT Gateway IP Address 104.233.121.78?

1 answer

KapilAnanth-MSFT 46,776 Reputation points Microsoft Employee

2024-04-08T06:28:13.39+00:00
@abeer hayat khan ,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.

May I ask how you are confirming 513.95.218.52 is a "Random MS Cloud address" ?

In fact, "513.95.218.52" is not even a valid IP Address, as we know IPV4 can only range between 0.0.0.0 to 255.255.255.255.

Moreover, it appears the IP which you have shared as NAT Gateway IP Address, "104.233.121.78" belongs to a 3rd party ISP and not Azure.
Can you share a screenshot of the Public IP from the Azure Portal, like below?

I would suggest you to please double-check your logs and give us more information as to what the exact issue is.

Cheers,

Kapil
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abeer hayat khan 0 Reputation points

2024-04-08T06:33:25.7133333+00:00

@KapilAnanth-MSFT sorry for that Ip are replaced by the original one. the SMTP logs is 52.101...* PIP is 20.110.*.**

KapilAnanth-MSFT 46,776 Reputation points Microsoft Employee

2024-04-08T06:44:40.5766667+00:00

@abeer hayat khan ,

Thanks for the info.

I take it that you have a VM in Azure, with NAT Gateway IP as 20.110.121.78.

This is connection to a relay server for SMTP in Internet, which logs the IP of the source VM as 52.101.218.52

Is this correct?

Can you also provide me some information on how the SMTP is configured in the VM?

Are you using Exchange Online Powershell Module?

Can you share any MS Documentation you used to set this up?

Cheers,

Kapil

abeer hayat khan 0 Reputation points

2024-04-08T06:56:00.7266667+00:00

@KapilAnanth-MSFT yes that correct

abeer hayat khan 0 Reputation points

2024-04-08T07:51:10.2566667+00:00

@KapilAnanth-MSFT We are receiving and able to send mail but the issue is random ip isntead of pip of Nat that were expected. we are using Eol relay

KapilAnanth-MSFT 46,776 Reputation points Microsoft Employee

2024-04-08T17:26:24.93+00:00

@abeer hayat khan ,

I would say this is an expected behavior.

Note that the IP 52.101.218.52 belongs to the Service Tag "EOPExternalPublishedIPs"

Use this to check IP's ranges : https://www.azurespeed.com/Azure/IPLookup

Service Tag docs : https://learn.microsoft.com/en-us/azure/virtual-network/service-tags-overview

From what the document says,

From the doc referenced here : Connect to Security & Compliance, it appears you are using Powershell to contact the Relay Server, and the traffic is not directly going from the VM

i.e., I think this is the behavior of the application rather than the VM itself.

P.S : My expertise with Exchange Online is limited.

I'd suggest posting a new question with appropriate "Exchange" tags so that community experts can provide more clarity on the issue.Or

You may file a support ticket where a support engineer can have a screen share session and provide more insights.

Cheers,

Kapil
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Azure Migrated Server - SMTP Traffic Bypassing NAT Gateway

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